1. Field of the Invention
The present invention relates to an actuator for automobiles.
2. Description of the Related Art
As a turbocharger for enhancing air intake efficiency of an internal combustion engine for automobiles, an exhaust gas-driven turbocharger that uses the flow of exhaust gas for supercharging is already available. The turbocharger includes a compressor wheel disposed in an air intake passage, and a turbine wheel, which is disposed in an exhaust passage, and rotates integrally with the compressor wheel. In the turbocharger having such a configuration, exhaust gas in the exhaust passage is introduced to the turbine wheel, thereby rotating the turbine wheel. The compressor wheel rotates with the rotation of the turbine wheel, thereby increasing the intake pressure (boost pressure) in the intake passage. As a result, it is made possible to forcibly introduce the intake air with high boost pressure into combustion chambers of the internal combustion engine, so that it is possible to enhance air intake efficiency of the internal combustion engine.
In order to prevent an excessive increase in boost pressure, an internal combustion engine provided with such a turbocharger generally has a bypass line for bypassing the turbine wheel provided on an exhaust line, and includes a wastegate for opening and closing the bypass line. An electrically-operated actuator for driving the wastegate is connected to the wastegate. When the boost pressure becomes equal to or higher than a predetermined pressure, part of the exhaust gas to be introduced to the turbine wheel is introduced into the bypass line by controlling driving of the actuator so as to open the bypass line. By introducing part of the exhaust gas to be introduced to the turbine wheel into the bypass line in this way, an excessive increase in the number of revolutions of the turbine wheel and the compressor wheel is prevented so that an excessive increase in boost pressure is avoided.
In a housing of the electrically-operated actuator as described above, a plurality of communication holes that allow the inside and the outside of the housing to communicate with each other are formed so as to ensure the ventilation of the inside of the housing. By ensuring the ventilation of the inside of the housing in this way, it is made possible to minimize condensation in the housing.
However, given that such communication holes are provided in the housing, when the automobile runs across a river, and the actuator is immersed into water, such a problem as described below cannot be treated lightly. Specifically, under the conditions in which the actuator is immersed into water, water enters the housing through the communication holes formed in the housing, which can cause a malfunction of the actuator.
Examples of such actuators include the actuator described in Japanese Utility Model Application Publication No. 5-42711 (JP-U-5-42711). In this actuator, a communication hole that allows the inside and the outside of the housing of the actuator communicate with each other is provided. Thus, when the actuator is immersed into water, water enters the housing, which can cause a malfunction of the actuator.
Other actuators of an internal combustion engine also have substantially the same problem in common that there is a possibility that an actuator malfunctions when the actuator is immersed into water, and water enters the housing. For example, the turbocharger described in Japanese Patent Application Publication No. 2005-256691 (JP-A-2005-256691) is provided with a movable vane for varying the flow rate of exhaust gas. The actuator for driving this movable vane also has a similar problem.